What are the three things the constitution obliges the national government to do for the states, and how are these obligations met?

The three things the Constitution obliges the national government to do for the states can be found Article IV. It is as follows:

That no new states would be created from a single state or neighboring states without the consent of the legislative approval of the state(s).

That no criminal shall enjoy refuge in any state. 

That the states are guaranteed a defense against invasion or insurrection and that the union of states shall always exist as a Republic.